The subject matter disclosed herein relates to semiconductor devices and, more specifically, to silicon carbide semiconductor devices.
For a semiconductor device, such as a silicon (Si) or silicon carbide (SiC) transistor, bias temperature instability (BTI) may cause substantial variability in device performance. For example, negative bias temperature instability (NBTI) in particular may result in a significant change or drift in the threshold voltage of a SiC device when operated under particular conditions, such as negative bias and/or elevated temperatures, over an extended period of time. The NBTI in SiC devices is thought to be a result of interfacial charge trapping (e.g., oxide charges), which may, for example, be induced by operating the device at an elevated temperature, and under a particular bias condition, for extended time periods. For example, a SiC metal-oxide-semiconductor field effect transistor (MOSFET) may experience a threshold voltage shift when subjected to combined voltage and temperature stressing due to NBTI.
In certain cases, the aforementioned NBTI may shift (e.g., decrease) the threshold voltage of a SiC device to the point that the device may become conductive even without an applied gate-source voltage, transforming a normally-off device into a normally-on device. As such, NBTI significantly impacts the reliability and performance of SiC devices. Considerable research has been directed toward designs to mitigate the BTI problem in Si devices, and, in certain instances, the BTI issue has been alleviated or obviated in Si. However, there are significant behavioral differences between Si and SiC devices and, therefore, the mechanisms used to alleviate the problem in Si do not readily translate to SiC. As such, an industry-accepted solution to NBTI in SiC devices has yet to be determined. Accordingly, alleviating the NBTI issue in SiC devices is especially desirable in order to take advantage of the unique operating characteristics (e.g., higher operating temperatures, improved mechanical properties, improved electrical properties, and so forth) that SiC may offer to certain systems and applications.